Among industrialized nations of the world, there is a growing concern for, and emphasis on, environmentally responsible practices. For example, more and more governments and communities are interested in minimizing the kinds and quantities of chemicals that are deposited into water systems, including wastewater systems. A common form of wastewater pollution is the alkali metals such as sodium and potassium discharged into sewers or septic systems during typical regeneration processes of water softeners.
For the last fifty years or so, water softening has become widely used in those regions where water supplies contain high concentrations of calcium and magnesium, and are therefore considered “hard”. Utilizing a sodium or potassium ion exchange process, resin-based water softeners are installed on water lines, particularly those leading into residences, to soften most if not all of the water used inside such homes. As a water supply passes through ion exchange resins inside a water softener, the calcium and magnesium ions bond to the resins and are removed from the water flow.
Periodically, these ion exchange resins must be regenerated by removing the hardness ions on the resins. Typically this regeneration is accomplished utilizing by washing the resins with an aqueous solution of alkali metal salts such as sodium or potassium chloride. The term “regenerant” in this application means “a liquid suitable for causing sodium or potassium to replace hardness ions on the surface of the softening resin.”
In a typical regeneration process, the regenerant is slowly pumped through the resin bed. Through a chemical exchange process, the calcium and magnesium ions which were adsorbed onto the resin during the softening process are stripped off the resins and replaced with sodium or potassium ions. At the conclusion of this process, the “spent” solution containing both the hardness ions and the regenerant is discharged into the sewer or septic system. It is this discharge that has serious long-term effects on the environment, as the regenerant salinity, total dissolved solids, and/or chloride cause corrosion in the sewage system, and contaminate the planet's fresh water supplies.
Presently, because this pollution problem has defied resolution by economically acceptable means, some communities are resorting to banning or limiting water softening in homes. For example, on Oct. 12, 2009, California governor Arnold Schwarzenegger signed into law, a bill giving local California water agencies the authority to restrict or even to ban the use of water softeners using on-site salt-based regeneration.
Scientific studies such as one conducted by Santa Clarita, Calif. are finding that regenerant discharged from water softeners is a significant source of water pollution. This finding supports prohibitions of, or restrictions on, current commercially available water softening systems. Consequently, removing the alkali salts from the spent regenerant before the solution is discharged has become an immediate and real concern both for communities that want soft water and for water softener manufacturers.